Humming sound from Rotel RT-1570 (USB-plugged in)

[RotelBorn]

Hi,

I'm new to this forum. First hit on Rotel Forum, was this site. I hope someone can help me.

Bought a Rotel RA-1570 (not RT) a few years ago, when it was new. And earlier this year I bought a USB-cable to connect my computer to it. because I wanted to try not using the Toslink I've used since the beginning.

Anyone, from my desktop computer I run the USB-cable to the back of the Rotel, then installed a set of Drivers.
It works! But I noticed a constant humming sound coming from all speakers (front, left, right). And the humming sound does not change with volume, it's pretty strong.

So, maybe the cause is the power lines between Desktop and the Stereo - I was smart, I hooked the Rotel up to a Laptop, and made it run on batteries = not interference with the power outlet. Still the same humming sound! Constant, not volume related.

Is my Rotel RA-1570 faulty? What else can I try?


/Bepps from Sweden

[wkhanna]

Welcome Bepps!

i am sure someone here will have some good advice for you soon.

[JonMarsh]

If it does it with a laptop running on batteries, it's most likely an issue with the USB receiver in your Rotel, or the power supply to the USB DAC built in (that's the most likely culprit, but that's just guessing, not knowing the internal layout). The only other additional test I can think of might be an iPhone or similar with the USB output converter.

Question- if you select the USB input, with nothing connected, do you still get the hum? Another thing to try is a USB cable with the power portion disconnected. You have tried other USB cables, right?

[RotelBorn]

Thanks you for your help. I mean: THANK YOU!, for your help.
Since I don't have any other USB-device and the right set of cables, I cannot try my smart phone as a source.

On the other hand, I did have a cheap "Printer USB-cable" that I could try using to my computer, to the Rotel USB.
Out with the expensive gold plated Supra Cable, and in with the cheaper one.

At first I thought - Oh My, this really was the issue, the cable was faulty. But when I moved the receiver back in again (in its stereo hole) the humming started again.

So, after looking really close at the cable socket at the back of the Rotel, I got the humming to stop by moving the cable exactly so much dead-centre it did not touch the socket metal parts.
As soon as the outer metal of the USB-cable came in contact with the socket of the Rotel, the humming started - and ends as soon as I adjust the cable so I does not touch.

I don't now what the metal part of the cable actually does (isn't it the four pins that transfer signals?)

After putting a few turn of tape around the cable end, to isolate the metal parts, the loud humming is gone!

But there still is a faint noise, like a "white noise" that disappears when I choose 0/no volume on the Rotel. It is also consistant and not a variable of volume. Static. Both computers does this, the noise is there regardless of what input I choose, maybe it just the Rotels silent humming and need for releasing it's power - I don't know. Will try identify where it is coming from.

[RotelBorn]

But there still is a faint noise, like a "white noise" that disappears when I choose 0/no volume on the Rotel. It is also consistant and not a variable of volume. Static. Both computers does this, the noise is there regardless of what input I choose, maybe it just the Rotels silent humming and need for releasing it's power - I don't know. Will try identify where it is coming from.

-> The only way I could find to get rid of the white noise was the unplug the two golden metal "U"-s from Pre-Out to Main-In, but - that must come with the draw back of zero sound.

[wkhanna]

glad to hear you got the big problem with the USB figured out.

the lower level noise may be RF or inherent in your incoming mains.
are you using any type of power conditioner?

[PewterTA]

To me, and Rotel is known for this, they don't always get the grounding "just right." By that I mean that they are very sensitive to the slightest grounding loop. My Rotel RSP-1098 has that issue on the Right pre-out of it that goes to the amps. The weird part is, I only have to disconnect it AT the Rotel RSP-1098 side and re-seat it and it works fine. Really odd, but it happens.

I would start by connecting just the speakers to the 1570 and see if you get any noise (if you turn the volume up you'll get some white noise from the power supply which is normal), but you should only hear that being a few inches from the tweeter on the speakers. If you get a noise from the unit, then I would say you need some type of power protection to help eliminate a ground loop. You could try another outlet to plug it into and see (I've been run an extension from another circuit over to verify if that changed anything or not.

If changing the outlet or better surge/filtration put in place fixes it, then something on that line is causing the feedback into the Rotel that you are hearing. Hopefully the changes fixed the problem for you though!

You could also, if you have something else that's grounded in your system... buy take a piece of cable and try attaching it to one of the chassis screws and then grounding the wire to another component that you know for sure has a good ground. People have had success with that!

I hope that helps!

-Dan